Patent Literature 1 discloses a conventional technique applied in an energy recovery system for recovering energy from a working fluid. The technique includes an inertial fluid container communicating with an outlet of an actuator, and a low pressure container and a high pressure container connected to the inertial fluid container in parallel. In addition, a low pressure valve which is a solenoid valve is disposed between the inertial fluid container and the low pressure container, and a high pressure valve which is a solenoid valve is disposed between the inertial fluid container and the high pressure container. In this energy recovery system, the high pressure valve is closed and the low pressure valve is opened to cause working fluid to flow from the inertial fluid container into the low pressure container. At this time, the flow of the working fluid generates fluid inertial forces in the inertial fluid container. Subsequently, the low pressure valve is closed and the high pressure valve is opened to cause the working fluid to flow into the high pressure container by the fluid inertial forces generated in the inertial fluid container. In this manner, the high pressure valve and the low pressure valve are opened and closed alternately at high frequency, thereby making it possible to recover the energy of the working fluid in the high pressure container.